Coil driver with high voltage switch

ABSTRACT

A coil driver circuit for ferrite phase shifters in a phased array antenna. The circuit provides for both slow and rapid changes between levels of coil current to effect changes in phase shift by means of a current-rate sensitive switch that momentarily applies a high-voltage to the coil when the current rate exceeds a particular value. This arrangement provides for a relatively low, average-power dissipation in the circuitry.

United States Patent [72] lnventor Joseph E. Bryden Framingham, Mass.

[21] Appl. No. 818,941

[22] Filed Apr. 24, 1969 [45] Patented June 1,1971

[73] Assignee Raytheon Company Lexington, Mass.

[54] COIL DRIVER WITH HIGH VOLTAGE SWITCH 6 Claims, 2 Drawing Figs.

1 [52] 1.1.8. Cl 317/148.5, 317/D1G.4 [51] Int. Cl H01h 47/32 [50] Field ofSearch 317/123 CD, 1485-123, 147; 307/104 [56] References Cited UNITED STATES PATENTS 2,941,125 6/1960 Lippincott 317/123 3,078,393 2/1963 Winston 317/123 3,149,244 9/1964 Barnes 307/104 3,158,791 11/1964 Deneen 3l7/148.5 3,183,412 5/1965 Arends 317/123 3,268,776 8/1966 Reed 3l7/148.5 3,339,120 8/1967 McGrath et a1... 317/148.5

3,361,939 2/1968 Smith 317/123 3,378,720 4/1968 Duerr et a1 315/27 Primary ExaminerL. T. Hiz Attorneys-Philip J. McFarland and Joseph D. Pannone ABSTRACT: A coil driver circuit for ferrite phase shifters in a phased array antenna. The circuit provides for both slow and rapid changes between levels of coil current to effect changes in phase shift by means of a current-rate sensitive switch that momentarily applies a high-voltage to the coil when the current rate exceeds a particular value. This arrangement provides for a relatively low, average-power dissipation in the circuitry.

COIL DRIVER WITH HIGH VOLTAGE SWITCII BACKGROUND OF THE INVENTION This invention relates to electric circuits for coil drivers, and more particularly to a relatively low power dissipation circuit providing a momentary high-voltage to the coil when rapid current changes are to be effected.

The drive coil of a ferrite phase shifter used in a phased array antenna is preferably energized from a continuously variable current source so that any phase shift within the operating range of the phase shifter can be provided. In a typical installation where hundreds and even thousands of phase shifters with their coil driver circuits are arranged closely spaced within an array, it is desirable to minimize power consumption within the individual coil driver circuits to prevent unnecessary heating of the antenna as well as to minimize the magnitude of the electric power supplies which energize the coil driver circuits. Since phased array antennas are particu' larly well adapted for rapid switching of the direction of the beam radiating from the antenna array, it is essential that the phase shifters which control the direction of the beam be capable of switching rapidly from one phase shift to another and accordingly, rapid changes of current are provided in the drive coils. Rapid current changes or transients in inductive loads such as phase shifter coils require considerable, and sometimes an inordinate amount of power supplied, or absorbed by, the driver circuit during the transient time as the stored energy in the coil is increased or decreased. Further, in phased array antenna applications, rapid changes in phase shift and coil current are required only at particular instants interspersed among periods of constant phase shift and coil current so that peak power need be supplied only momentarily while the average power required may be considerably lower.

It is therefore an object of the present invention to provide a coil driver circuit for a ferrite phase shifter providing a continuously variable current for the phase shifter coil.

A further object of the invention is to provide a coil driver circuit capable of producing rapid changes in coil current with a relatively low average power dissipation.

SUMMARY OF THE INVENTION To a circuit having a current source, a first source of electric power, and a coil which are connected whereby a current from such source energizes the coil, there is connected additional circuitry in accordance with the invention by which a second, and larger, source of electric power is connected, via a switching arrangement which disconnects the first source of electric power, to permit the coil to be energized from the second source during periods of rapid change in coil current. A sensing circuit is provided for sensing the rate of change of the coil current and operating the switching arrangement when the rate of change exceeds a particular value. Means are also provided for connecting the second source with the coil to effect a rapid deenergization of the coil.

BRIEF DESCRIPTION OF THE DRAWING The aforementioned objects and other featu res of the invention are explained in the following description taken in connection with the accompanying drawing wherein:

FIG. 1 is a partial view of a phased array antenna in diagrammatic form showing a plurality of phase shifter elements and the relationship of a drive circuit in accordance with the invention to one of the phase shifter elements; and

FIG. 2 is an electrical schematic diagram of a preferred embodiment of the invention,

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, there is shown a partial view, in diagrammatic form of the relevant portions of a phased array antenna 4 having ferrite phase shifter elements 5 positioned by support structure 6. A horn 7, also positioned by support structure 6 and connecting with a transmitter, not shown, illuminates the phase shifting elements with electromagnetic radiation. As is well known, each ferrite phase shifter element 5 imparts a phase shift to electromagnetic radiation in accordance with the strength and sense of a magnetic field supplied by a coil 8 within each ferrite phase shifter element 5. The coil 8 is energized by coil current conducted along electrical conductors 9A and 98 from a coil driver circuit 10 of the invention which is shown in detail in FIG. 2. As shown in FIG. 1 and FIG. 2, coil driver circuit 10 has a current controller 1] which in response to an input signal 12 generated by a computer, not shown, controls the magnitude of the coil current in its steady state and during relatively small rates of change in coil current to provide the desired phase shift to the electromagnetic radiation. The coil current is supplied through a switch 13 from with power supply 14 (here shown having a voltage V,) or power supply 15 (here shown having a voltage V greater than V,). A sensing circuit 16, responsive to the rate of change of coil current in one direction at current controller 11, operates switch 13 to connect either power supply 14 or power supply 15 in accordance with the rate of change of the coil current. A second switch, switch 19, operative when the coil current is rapidly changing in the direction opposite from the just-mentioned case, connects power supply 15 to the circuit to effect a rapid change of current through coil 8.

Referring now to FIG. 2, there is a schematic diagram showing the preferred embodiment of the invention in which the ferrite phase shifter coil 8 is energized with current by current controller 11 and power supply 14. Switch 13, to be described hereinafter, has a transistor 20 and diode 21 for respectively connecting voltage V and disconnecting voltage V, in accordance with the invention. Sensing circuit 16 of the invention, utilizing transistor 22, is sensitive to the rate of change of coil current and operates switch 13 by turning transistor 20 ON or OFF in a manner to be described. Switch 19 comprising diode 24 aids in deenergizing coil 8 as described hereinafter by supply an auxiliary conductor path to power supply 15.

Current controller 11 is composed of a transistor 26, normally conducting and having emitter electrode 28, base electrode 30, and collector electrode 32, a well-known operational amplifier 34, emitter resistor 36, and summing resistors 38 and 40 for respectively summing input signal 12 with a feedback signal at point 44. Operational amplifier 34 is connected to power supplies, not shown, and to ground 46 by a conductor, not shown, and supplies base current to base electrode 30 of transistor 26 in accordance with the magnitude of input signal 12. The emitter current in emitter electrode 28 and collector current in collector electrode 32 are proportional to the base current in base electrode 30, as is well known, so that the voltage at point 44 developed across emitter resistor 36, which has a small value such as 10 ohms to preserve circuit linearity, is representative of the emitter current and therefore a suitable signal for feedback around the operational amplifier. The output of the current controller 11 is the collector current at collector electrode 32 which is linearly related to the input signal 12 because of the feedback and is substantially independent of the voltage V, for the values of V, within the range of values for linear operation of transistor 26.

Phase shifter coil 8 presents a reactive load to the circuit and has both inductance, typically on the order of 50 millihenries, represented by inductor 48 and resistance, generally less than 50 ohms, represented by resistor 50. Diode 21, coil 8, transistor 26 and emitter resistor 36 are connected in series between power supply 14 and ground 46. In this embodiment, transistor 26 is a PNP type and V, is negative with respect to ground so that current flows from the emitter electrode 28 to collector electrode 32 towards power supply 14.

The sensing circuit 16 is composed of transistor 22, normally conducting and having emitter electrode 52, base electrode 54 and collector electrode 56, resistor 58 providing a current path between base electrode 54 and power supply 14, resistor 60 providing a current path between collector 56 and power supply 62 having a voltage V and diode 64 through which the sensing circuit is connected to the junction of coil 8 and transistor 26. Transistor 22 is a PNP type so that current from power supply 66 having a voltage V flows into emitter electrode 52 and then splits with one portion flowing out of base electrode 54 into resistor 58 which sets the quiescent base current, and a second portion of the emitter current flowing out of collector electrode 56 into resistor 60 which sets the quiescent voltage level across transistor 22. The four power supplies l4, 15, 62 and 66 each have one terminal grounded so that their four voltages, respectively, V,, V V and V, are referenced to ground 46. Voltage V is negative with respect to ground and positive with respect to V,. Voltage V:, is negative and equal in magnitude to voltage V during the basic operation of the circuit of FIG. 2; however, it can be reduced in magnitude in a manner to be described below.

The voltage V,, having a value typically of a few volts, establishes the sensing level for sensing the magnitude of the rate of change of coil current in coil 8. When the coil current is constant, that is, zero rate of change, the voltage drop across coil 8 is minimal causing the collector voltage of collector electrode 32 of transistor 26 to have a relatively large negative voltage relative to the voltages of the base electrode 54 and emitter electrode 52 of transistor 22 so that diode 64 is backbiased and nonconducting. When, in response to signal 42, the coil current is increasing, the voltage drop across coil 8 increases thereby reducing the back bias across diode 64. For large values of voltage drop across coil 8, the voltage of collector electrode 32 is positive with respect to the voltage of base electrode 54 so that diode 64 conducts and applies a reverse voltage bias across the base emitter junction of transistor 22 thereby cutting off the current flow through transistor 22.

The sensing circuit operates the switch composed of diode 21, transistor 20, normally nonconducting and having emitter electrode 68, base electrode 70 and collector electrode 72, and resistor 74 which provides base current to base electrode 70. Transistor is a PNP type, and accordingly, current flows from emitter electrode 68 through base electrode 70 and into resistor 74 when the voltage at junction 76 of resistor 74, collector electrode 56 and resistor 60 is negative with respect to the voltage at base electrode 70. The voltage drop across resistor 60 depends on the conduction state of transistor 22 and, accordingly, the voltage at junction 76 has a small value when transistor 22 is conducting and a large negative value when transistor 22 is cut off. Thus, when transistor 22 is conducting, the base emitter junction of transistor 20 is back-biased and transistor 20 is cut off; and when transistor 22 is cut off, transistor 20 is conducting.

In operation, therefore, when a rapid change of coil current causes the voltage drop across coil 8 to increase to such a value that collector electrode 32 of transistor 26 is positive with respect to base electrode 54 of transistor 22, transistor 22 is cut off and the voltage of junction 76 increases to a large negative value causing transistor 20 to conduct. The conduction of transistor 20 establishes at point 78, the junction of emitter electrode 68, diode 21 and coil 8, a large negative voltage of magnitude V minus the voltage drop across transistor 20. Thus, the voltage at point 78 is driven negative with respect to V, and diode 21 is back-biased in a state of nonconduction. The coil 8 is therefore energized by means of the higher voltage V rather than voltage V, to effect a rapid change in coil current. As the coil current reaches the level dictated by signal 12, the rate of change of coil current decreases, the voltage drop across coil 8 decreases and the above process is reversed so that transistor 20 is again out off and coil 8 is energized by V,.

For decreasing values of coil current the voltage drop across coil 8 increases with a polarity opposite to that described above. Thus collector electrode 32 of transistor 26 is driven further negative, diode 64 remains in a state of nonconduction, and the conduction states of transistors 22 and 20 remain unchanged. With very rapid decreases in coil current, collector 32 is driven sufficiently negative to apply a forward voltage bias across diode 24 bringing it into a state of conduction so that the stored magnetic energy in coil 8 is absorbed by power supply 15 as the coil current passes through diodes 24 and 21. Power supply 15 also serves to limit the maximum voltage developed across coil 8 thereby preventing damage to the components of the circuit. When the coil current drops to the level dictated by signal 12, the rate of change of coil current is reduced, and the voltage drop across coil 8 is reduced thereby back-biasing diode 24 so that the coil 8 is disconnected from V With this arrangement, diode 24 in conjunction with collector 32 and base 54 serves as both a sensing and switching device responsive to the voltage drop across coil 8.

As an example of voltage levels which are convenient for controlling the coil current in ferrite phase shifter coil 8 during typical operation in a phase array antenna, V, has a magnitude on the order of ten volts and V has a magnitude on the order of volts. Thus it is clear that during a rapid decrease in coil current, when diode 24 is conducting, power supply 14 has little effect on the circuit and, by way of example, could be momentarily bypassed by a short circuit. Due to the relatively large swings in voltage experienced by the transistors 20 and 22, diodes, not shown, are connected in a well-known manner across the base emitter junctions of these transistors, such that current flows through the diodes when the base emitter junctions are back-biased, thereby protecting these junctions from excessive inverse voltage.

During typical phased array antenna operation wherein rapid coil current changes are interspersed among periods of constant coil current, the voltage V, may alternatively be reduced, as by using a programmable power supply, during the periods of constant coil current thereby affording a saving in the average power supplied to the circuit. The circuit is particularly adapted for this power saving since transistor 20, being nonconducting during periods of constant coil current, draws no power from supply 15; and similarly transistor 22 can operate from a low voltage supply during periods of constant coil current thereby dissipating less power in resistor 60.

The circuit is also particularly adapted for use in a phased array antenna in which a multitude of these circuits are simultaneously employed. In such a situation it is anticipated that switching transients introduced by one circuit are transmitted to neighboring circuits and accordingly it is desirable that a circuit should be substantially insensitive to power supply voltage fluctuations induced by these switching transients. The current provided by transistor 26 to coil 8 is substantially independent of fluctuations in voltage V, since, as is well known, the current through a transistor utilized in a standard amplifier circuit depends mainly on the base-emitter voltage and varies only slightly with the base-collector voltage. Fluctuations in V V and V, are of little import since these voltages play a role only during rapid changes in the coil current.

The use of two power supplies greatly reduces the average power required to supply coil current. For example, if a single supply were utilized, it would have a voltage V in order to supply the same maximum current rate of change that is supplied by the circuit of FIG. 2. However, V is typically 10 times greater than V, resulting in approximately 100 times as much power being supplied to such a coil driver circuit during periods of constant coil current. The circuit of FIG. 2 provides for a switching to a supply having high voltage only when the high voltage is required for effecting rapid changes in the coil current.

In the circuit of FIG. 2, the coil is directly coupled to sensing and switching circuitry rather than by means of transformer coupling as is done in some circuits of the prior art. Thus the present circuit is free of a frequency dependence such as is associated with transformer coupling and is readily set to respond either to a fast or slow rate of coil current change simply by selecting the magnitude of voltage V,.

The present circuit is adapted particularly for a ferrite phase shifter coil employed in a phased array antenna. However, the circuit can be used to drive other forms of inductive loads such as a dynamic focusing coil or a deflection coil in a cathode ray tube or a small electric motor.

It is understood that the above-described embodiment of the invention is illustrative only and that modifications thereof will occur to those skilled in the art. For example, the circuit could be replaced with its complimentary circuit using NPN- type transistors instead of PNP-type transistors and reversed polarities of power supply voltages. Accordingly, it is desired that this invention is not to be limited to the embodiment disclosed herein but is to be limited only as defined by the appended claims.

Iclaim:

l. A circuit for controlling current in a coil comprising:

A first switching means and a first source of power serially connected with the coil for energizing the coil with an electric current;

A second source of power connected to the first switching means; and

Sensing means responsive to the rate of change of current in the coil, the sensing means operating the first switching means to provide alternate states of conduction such that when a positive rate ofchange ofcurrent in the coil is less than a first predetermined value, the coil is energized with power from the first source of power and when the positive rate of change of current in the coil is greater than the first predetermined value, the coil is energized with power from the second source of power.

2. The circuit as defined by claim 1 wherein the sensing means comprises:

transistor circuit means providing a switching control signal for the first switching means; and

a diode in circuit between the coil and the transistor circuit means, the diode being in a state of conduction when the rate of change of current in the coil is greater than the first predetermined value.

3. The circuit as defined by claim 1 wherein the first source of power has a first voltage and the second source of power has a second voltage greater than the first voltage, the circuit further comprising a second switching means interconnecting the coil and the second source of power, the second switching means being operative in response to the rate of change of current in the coil such that when a negative rate of change of current in the coil attains a second predetermined value, stored energy within the coil is discharged through the second switching means into the second source of power.

4. The circuit as defined by claim 3 wherein the sensing means comprises:

transistor circuit means providing a switching control signal for the first switching means; and

a diode in circuit between the coil and the transistor circuit means, the diode being in a state of conduction when the rate of change of current in the coil is greater than the first predetermined value.

5. In a phased array antenna utilizing a plurality of phase shifting elements, each of which incorporates a coil and provides a phase shift in accordance with computer commands, an improved coil driving circuit for the coils responsive to independent input signals from the computer for individual control of the current in each of the coils comprising:

current controller means responsive to the input signals from the computer:

a first switching means and a first source of power: the current controller means, the first switching means and the first source of power being serially connected with the coils for energizing the coils with electric currents:

a second source of power connected to the first switching means; and SENSING MEANS RESPONSIVE T0 THE RATES OF CHANGE OF CURRENTS IN THE COILS,

THE SENSING MEANS OPERATING THE FIRST SWITCHING MEANS TO PROVIDE ALTERNATE STATES OF CONDUCTION SUCH THAT WHEN A POSITIVE RATE OF CHANGE OF CURRENT IN THE COIL IS LESS THAN A FIRST PREDETERMINED VALUE, THE COIL IS ENERGIZED WITH POWER FROM THE FIRST SOURCE OF POWER AND WHEN THE POSITIVE RATE OF CHANGE OF CURRENT IN THE COIL IS GREATER THAN THE FIRST PREDETERMINED VALUE, THE COIL IS ENER- GIZED WITH POWER FROM THE SECOND SOURCE OF POWER.

6. The circuit as defined by claim 5 wherein the first source of power has a first voltage and the second source of power has a second voltage greater than the first voltage, the circuit further comprising a second switching means interconnecting the coils and the second source of power, the second switching means being operative in response to the rates of change of currents in the coils such that when the negative rates of change of currents in the coils attain a second predetermined value, stored energy within the coils is discharged through the second switching means into the second source of power.

Page 1 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 582, 734 Dated June 1, 197].

Inventor(s) Joseph E. Bryden It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION Column 1, line 42, change "SUMMARY OF THE INVENTION 0" to SUMMARY OF THE INVENTION Column 2, line 15, change 'with" to either Column 2, line 38, change "by supply" to by supplying IN THE CLAIMS Column 6, Claim 5, line 15, change Q to Column 6, Claim 5, line 19," change g to Column 6, Claim 5, lines 21 to 34, change:

"means; and SENSING MEANS RESPONSIVE TO THE RATES OF CHANGE OF CURRENTS IN THE COILS, THE SENSING MEANS OPERATING THE FIRST SWITCHING MEANS TO PROVIDE ALTERNATE STATES OF CON- DUCTION SUCH THAT WHEN A POSITIVE RATE OF CHANGE OF CURRENT IN THE COIL IS LESS THAN A FIRST PREDETERMINED VALUE, THE COIL IS ENERGIZED WITH POWER FROM THE FIRST SOURCE OF POWER AND WHEN THE POSITIVE RATE OF CHANGE OF CURRENT IN THE COIL IS GREATER THAN THE FIRST PREDETERMINED VALUE, THE COIL IS ENERGIZED WITH POWER FROM THE SECOND SOURCE OF POWER."

FORM PC4050 USCOMM-DC 60375-Pb9 i [L5 GOVERNMENT PRINTING OFFICE. 19.9 0-156-331 Page 2 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3.582.734 Dated June 1, 1971 Inventor(s) Joseph E. Bryden It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

means; and

sensing means responsive to the rates of change of currents in the coils, the sensing means operating the first switching means to provide alternate states of conduction such that when a positive rate of change of current in the coil is less than a first predetermined value, the coil is energized with power from the first source of power and when the positive rate of change of current in the coil is greater than the first predetermined value, the coil is energized with power from the second source of power.

Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSOHALK Atteating Officer Commissioner of Patents FORM Flo-1050 (10459) USCOMM-DC QOB'IG-PQD 9 Us. GOVIINHINT PRINTING OFF-1C I 1.. 0"!633. 

1. A circuit for controlling current in a coil comprising: A first switching means and a first source of power serially connected with the coil for energizing the coil with an electric current; A second source of power connected to the first switching means; and Sensing means responsive to the rate of change of current in the coil, the sensing means operating the first switching means to provide alternate states of conduction such that when a positive rate of change of current in the coil is less than a first predetermined value, the coil is energized with power from the first source of power and when the positive rate of change of current in the coil is greater than the first predetermined value, the coil is energized with power from the second source of power.
 2. The cIrcuit as defined by claim 1 wherein the sensing means comprises: transistor circuit means providing a switching control signal for the first switching means; and a diode in circuit between the coil and the transistor circuit means, the diode being in a state of conduction when the rate of change of current in the coil is greater than the first predetermined value.
 3. The circuit as defined by claim 1 wherein the first source of power has a first voltage and the second source of power has a second voltage greater than the first voltage, the circuit further comprising a second switching means interconnecting the coil and the second source of power, the second switching means being operative in response to the rate of change of current in the coil such that when a negative rate of change of current in the coil attains a second predetermined value, stored energy within the coil is discharged through the second switching means into the second source of power.
 4. The circuit as defined by claim 3 wherein the sensing means comprises: transistor circuit means providing a switching control signal for the first switching means; and a diode in circuit between the coil and the transistor circuit means, the diode being in a state of conduction when the rate of change of current in the coil is greater than the first predetermined value.
 5. In a phased array antenna utilizing a plurality of phase shifting elements, each of which incorporates a coil and provides a phase shift in accordance with computer commands, an improved coil driving circuit for the coils responsive to independent input signals from the computer for individual control of the current in each of the coils comprising: current controller means responsive to the input signals from the computer: a first switching means and a first source of power: the current controller means, the first switching means and the first source of power being serially connected with the coils for energizing the coils with electric currents: a second source of power connected to the first switching means; and SENSING MEANS RESPONSIVE TO THE RATES OF CHANGE OF CURRENTS IN THE COILS, THE SENSING MEANS OPERATING THE FIRST SWITCHING MEANS TO PROVIDE ALTERNATE STATES OF CONDUCTION SUCH THAT WHEN A POSITIVE RATE OF CHANGE OF CURRENT IN THE COIL IS LESS THAN A FIRST PREDETERMINED VALUE, THE COIL IS ENERGIZED WITH POWER FROM THE FIRST SOURCE OF POWER AND WHEN THE POSITIVE RATE OF CHANGE OF CURRENT IN THE COIL IS GREATER THAN THE FIRST PREDETERMINED VALUE, THE COIL IS ENERGIZED WITH POWER FROM THE SECOND SOURCE OF POWER.
 6. The circuit as defined by claim 5 wherein the first source of power has a first voltage and the second source of power has a second voltage greater than the first voltage, the circuit further comprising a second switching means interconnecting the coils and the second source of power, the second switching means being operative in response to the rates of change of currents in the coils such that when the negative rates of change of currents in the coils attain a second predetermined value, stored energy within the coils is discharged through the second switching means into the second source of power. 